The colour coded boxes are a feature allowing you to see at a glance when you last had contact with your contacts using colour coding.

Green shows contact from 1-30 days

Amber from 31-90 days

Red from 90+ days.

This is a great way to see any contacts that you have not touched base with for a while.  Any contacts without a colour coded box showing will mean that the contact record has been active that day, i.e. today.